In human amniotic fluid, prolactin (hPRL) concentrations exceed those of maternal plasma in the first half of gestation by as much as 100-fold. Unkeratinized fetal skin is permeable to and actively participates in the transfer of water and electrolytes. Amnion and chorion do so as well. In studies just completed, human amnion reduces the transport of tritiated water to the maternal side. In addition, experiment with fetal skin from the subhuman primate indicate that prolactin has no effect on such transfer, that is, from amniotic fluid side to fetal side. The present proposal is designed to measure changes in water transport from the fetal to the amniotic fluid side of fetal skin in subhuman primates and in fetuses aborted prior to the 20th week of gestation. In addition, water transport across human amnion, chorion and chorioamnion will be studied. Since a specific effect of prolactin has been identified on human amnion, attempts will be made to isolate specific prolactin membrane receptors from human amnion and chorion and to quantitate these receptors. The detection of fetal pituitary maturation for prolactin secretion will also be correlated with the peripheral concentration of fetal PRL, amniotic fluid PRL and the keratinization of human skin.